Oven with humidity conditioner

Abstract: An oven with a humidity conditioner is capable of cooking food by appropriately humidifying or dehumidifying it while the amount of steam contained in an oven cavity is being regulated. The oven includes a heater or magnetron for heating the food accommodated in the oven cavity, a humidity regulator for regulating the humidity inside the oven cavity, a cooking method selector for selecting a cooking method, and a controller for controlling the humidity regulator in response to a signal from the cooking method selector to selectively humidify and dehumidify the interior of the oven cavity.

Description: Field of the Invention The present invention relates generally to an oven such as a microwave oven, a cooking range or the like and, more particularly, to an oven with a humidity conditioner capable of cooking food by appropriately humidifying or dehumidifying it, i. e., by appropriately regulating the amount of moisture. Description of Related Art US-A-4 924 072 representing the closest prior art from which the invention proceeds discloses a combination steam and dry oven having an integral boiler which is located inside the oven cavity. The combination oven can be operated as a forced-air convection oven, a force convection oven circulating superheated steam, or a steamer near the boiling temperature of water. Sensors in the oven supply information to a microprocessor which controls heating elements to maintain an oven temperature within a predetermined temperature range. The oven functions by circulating superheated steam by blowing its circulating gas over the surface of the internal boiler which is protected from contamination by a baffle. Sensors of the level of water in the boiler assure that the water level either stays within predetermined limits or else shuts down the oven if the water level is out of limits. Tray stops keep foods and the trays containing them away from the walls of the oven to permit free circulation of air or superheated steam. Sensors of water temperature in the boiler and gas temperature in the circulating gas permit the control of relative humidity when the oven is used to proof dough or hold cooked food at a relatively low temperature. Control of the temperature of water in the boiler is aided by blow-down and replacement of the temperature becomes excessive. Accordingly, in this conventional oven the regulating of humidity is performed by means of the boiler which evaporates steam (humidifying) or by draining water (dehumidifying). From US-A-4 835 351, it is known an oven comprising a cabinet having a plurality of cooking cavities, air recirculating units for circulating air through each cooking cavity, and a humidity control apparatus for controlling humidity of air circulated through the cavity. Programmable controls regulate air flow through the recirculating units to provide controlled pulses of air of controlled temperature and humidity to provide a desired surface moisture content. The humidifying is caused by means of air flowing along a water tray, whereas the dehumidifying is brought about by venting air. EP-A-0 000 957 discloses a microwave oven sensing system having a humidity sensor and a temperature sensor at an exit ventilation port of a microwave oven heating cavity to detect the exiting humidity and the air temperature of the microwave oven heating cavity. The sensors connect to a programmable controller and input the detected humidity and temperature of the microwave oven heating cavity to a programmable controller. Characteristic humidity curves for microwave cooking of different types of foods are stored in the memory of the programmable controller, and the programmable controller controls the microwave cooking in accordance with a selected algorithm for the detected environmental conditions. A numeric keyboard control panel inputs to the programmable controller the microwave cooking parameters and selects the desired characteristic humidity curve. The programmable controller may control a microwave power source control circuit and an air exchange circuit according to the selected algorithm in the programmable controller. In this conventional system, the humidifying and dehumidifying is caused by venting air. A further conventional microwave oven which is in wide practical use today is shown in Fig. 1. The oven of Fig. 1 has a casing 101 accommodating a turntable 102, on which food 103 is placed for subsequent induction heating. Reference numeral 105 denotes a motor for driving the turntable 102. A magnetron 106, employed as a microwave supply means, effects microwave heating with the use of high-frequency microwaves of, for example, 2,450 MHz. The microwaves emitted from the magnetron 106 are supplied into an oven cavity 104 through a waveguide 107 to heat the food 103. When the magnetron 106 receives high-voltage electric power from a drive unit 108, it oscillates to generate the high-frequency microwaves. Reference numeral 109 denotes a cooling fan for cooling elements that generate heat. The conventional microwave oven of the above-described construction is designed to cook the food 103 by heating it from inside by induction heating, and is characterized by very easy and quick reheating or warming and melting of food. On the other hand, the recent food life has been changed drastically under the influence of social changes, and in particular, the progress in manufacturing, storing and transporting technology of frozen food and chilled food has promoted the distribution and spread of cooked foods and other similar foods. Therefore, the recent food life has been changed to the simple and rational tendency represented by the cooked food, and the demands for cooking apparatus have been shifted mainly to cooking by reheating. In such circumstances, the conventional oven was not sufficient for cooking by reheating because of its heating mechanism. That is, there are a variety of cooked foods including oily foods such as fries food and tempura, vegetable foods such as fresh vegetables and boiled vegetables, stewed foods, and steamed foods. It is now hard to reproduce sufficiently the original taste of the food material or cook healthfully while maintaining nutrients only by heating with microwaves, and an oven capable of reheating depending on the conditions of food materials has been demanded. At the same time, the frozen foods are varied in shape and increased in combination of materials, and thawing by a microwave oven tends to cause uneven heating due to difference in the microwave absorbing characteristic. Accordingly, a cooking apparatus having superior thawing performance has been demanded. Fig. 2 depicts a conventional combination oven. In high-frequency heating, a drive unit (not shown) supplies a high-frequency oscillator 106 with high-voltage electric power to cause it to oscillate and generate high-frequency microwaves. The high-frequency microwaves generated by the high-frequency oscillator 106 are supplied into the oven cavity 104 through a waveguide 107 to heat food 103 on the turntable 102. During heating, heat generated by a heater 110 is used to heat the food 103 by infrared radiation or convection. In the above-described construction, however, when cooked rice is reheated, for example, as the food is heated, moisture in the food is vaporized, and the food surface is dried and hardened. To remedy such a defect, a combination oven with a steam generator as shown in Fig. 3 has been proposed. The oven of Fig. 3 is provided with a steam generator 112 comprised of a water tank 113 and a heater 111, in addition to the construction of Fig. 2. Food 103 placed on the turntable 102 inside the oven cavity 104 is heated by high-frequency microwaves that are generated by the high-frequency oscillator 106 and introduced into the oven cavity 104 through the waveguide 107. Moreover, the water in the steam generator 112 is converted, by the heater 111, into steam 114, which is introduced into the oven cavity 104 to prevent the food 103 from being dried during cooking. On the other hand, when fried food is reheated, the food is heated while the water content on the food surface is being increased due to migration of moisture onto the food surface caused by vaporization of moisture inside the food, and also due to a reduction in speed of vaporizing from the food surface caused by humidity elevation in the oven cavity. In this construction, however, since the steam generator 112 comprised of the heater 111 and the water tank 113 is separately provided, water feed into the steam generator 112 and treatment of drain water are troublesome. Furthermore, when the fried food is reheated, the food surface becomes damp due to increase of moisture on the food surface in the heating process, and crisp and fresh finish is not expected. SUMMARY OF THE INVENTION The present invention has been developed to overcome the above-described disadvantages. It is accordingly an objective of the present invention to provide an oven with a humidity conditioner capable of cooking food while humidifying it without supply of water or treatment of drain water, and also capable of cooking the food while dehumidifying it depending on the kind of food. Another objective of the present invention is to provide an oven with a humidity conditioner capable of humidifying or dehumidifying as desired during cooking, while regenerating an adsorbent necessary for humidifying and dehumidifying within a short period of time. A further objective of the present invention is to provide the oven of the above-described type which not only exhibits superior cooking abilities by supplying a wide variety of food with optimized steam, but also enables automatic cooking while ensuring high heating performance, enhanced airtightness, and enhanced safety. In accomplishing the above and other objectives, the oven according to the present invention comprises an oven cavity defined therein in which food to be cooked in to be accomodated, said oven further more comprises a food heating means for heating the food accommodated in the oven cavity, a humidity regulating means for regulating a humidity inside the oven cavity, a cooking method selecting means for selecting a cooking method, and a control means for controlling the humidity regulating means in response to a signal from the cooking method selecting means to selectively humidify and dehumidify an interior of the oven cavity. The humidity regulating means comprises adsorption means for absorbing or emitting steam contained in the air. By the above-described construction, upon placement of the food inside the oven cavity, when the cooking method is selected by the cooking method selecting means, the control means controls the humidity regulating means in response to the signal therefrom so that the food may be appropriately heated while steam contained in the oven cavity is adsorbed by the steam adsorption means or the steam is emitted therefrom into the oven cavity. Advantageously, the humidity regulating means comprises an internal suction port facing the oven cavity, an internal discharge port facing the oven cavity, a circulation duct for communicating the internal suction port and the internal discharge port with each other, a blower for sending air to the steam adsorption means, and a heat supply means for supplying the steam adsorption means with thermal energy. In this case, the steam adsorption means is accommodated in the circulation duct. According to this construction, when the food is cooked while being humidified, a moisture adsorbing process is carried out prior to cooking or at the end of cooking without requiring supply of water or treatment of drain water. In the moisture adsorbing process, the control means causes the steam adsorption means to adsorb moisture contained in the air in response to a signal indicative of "humidified cooking" selected manually or automatically by the cooking method selecting means. On the other hand, when the food is cooked while being dehumidified, a regeneration process is carried out prior to cooking or at the end of cooking. In the regeneration process, the control means causes the steam adsorption means to emit moisture contained therein in response to a signal sent manually or automatically from the cooking method selecting means. Preferably, the humidity regulating means comprises an internal suction port facing the oven cavity, an external suction port facing the outside of the oven cavity, a suction duct for communicating the internal suction port and the external suction port with each other, a suction port switching member accommodated in the suction duct, an internal discharge port facing the oven cavity, an external discharge port facing the outside of the oven cavity, a discharge duct for communicating the internal discharge port and the external discharge port with each other, a discharge port switching member accommodated in the discharge duct, a communication duct for communicating the suction duct and the discharge duct with each other, a blower for sending air to the steam adsorption means, and a heat supply means for supplying the steam adsorption means with thermal energy. In this case, the steam adsorption means is accommodated in the communication duct. In the humidified cooking process, on the basis of a signal indicative of "humidified cooking" selected manually or automatically by the cooking method selecting means, the control means switches, prior to cooking or at the end of cooking, the suction port switching member and the discharge port switching member to open the external suction port and the external discharge duct, respectively. By so doing, moisture contained in the air outside the oven cavity is adsorbed by the steam adsorption means. After this adsorption process, steam is generated within a short period of time by switching the suction port switching member and the discharge port switching member to open the internal suction port and the internal discharge duct, respectively, and by supplying the heat supply means with electric power, and also by operating the blower. Thus, desired humidified cooking is realized in which the moisture outside the oven cavity is freely utilized. In the case of dehumidified cooking, the control means switches both the switching members so as to carry out the regeneration process within a short period of time, with the generated steam discharged outside the oven cavity. Furthermore, because the food accommodated in the oven cavity can be heated with steam at a desired temperature, steam heating at a low temperature of about 60 to 70°C, steam heating at about 100°C, dry steam heating at about 150 to 200°C, and their combined heating can be effected depending on the kind and quantity of food. Heat transfer by steam enables heating at a high heat flow rate, as compared with ordinary heat transfer by air, thus enabling high-speed heating. Also, because dry steam heating, wet steam heating, and their combined heating are possible, uniform and appropriate heating is achieved at a relatively high speed depending on the kind and quantity of food. Alternatively, the humidity regulating means comprises an internal suction port facing the oven cavity, an internal discharge port facing the oven cavity, a circulation duct for communicating the internal suction port and the internal discharge port with each other, a blower for sending air to the steam adsorption means, and a high-frequency supply means for supplying the steam adsorption means with high frequency. In this case, the steam adsorption means is accommodated in the circulation duct. According to this construction, by supplying the high-frequency supply means with electric power and by operating the blower, humidified cooking can be realized in which steam is generated within a short period of time. Also, after the regeneration process in which moisture contained in the steam adsorption means is emitted therefrom within a short period of time, dehumidified cooking can be carried out. When the heat supply means or the high-frequency supply means is employed to apply energy to water molecules contained in the steam adsorption means to thereby emit moisture therefrom, the water molecules adsorbed thereby from the air is converted to steam. By so doing, water can be supplied from the air automatically, and the user can save time to replenish water. Also, condensation of steam in the oven cavity is avoided by adsorbing again the steam once discharged into the oven cavity, thereby preventing flooding in the oven cavity, and corrosion and trouble of the appliance. The steam adsorption means may contain a magnetic or metallic material, and the humidity regulating means may comprise an exciting means for applying thermal energy to the magnetic or metallic material. In this case, energization of the exciting means renders the steam adsorption means to emit moisture adsorbed thereby to generate steam. This construction is particularly effective because the thermal energy applied to the magnetic or metallic material heats the steam adsorption means itself, realizing a highly efficient water-molecule separation. Advantageously, the exciting means comprises an induction-heating means. The induction-heating means applies thermal energy to the steam adsorption means without contacting it, to thereby emit water molecules therefrom to generate steam. Furthermore, the steam adsorption means and the induction-heating means can be separated and insulated from each other, thus enhancing safety and airtightness and providing a highly efficient oven that can be readily manufactured at a low cost. A heater may be interposed between the oven cavity and the humidity regulating means to allow the humidity regulating means to easily emit moisture when air heated by the heater passes through the humidity regulating means. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objectives and features of the present invention will become more apparent from the following description of preferred embodiments thereof with reference to the accompanying drawings, throughout which like parts are designated by like reference numerals, and wherein: Fig. 1 is a schematic vertical sectional view of a conventional microwave oven; Fig. 2 is a schematic vertical sectional view of a conventional combination oven; Fig. 3 is a schematic vertical sectional view of another conventional combination oven; Fig. 4 is a schematic vertical sectional view of an oven according to a first embodiment of the present invention; Fig. 5 is a schematic vertical sectionai view of the oven of Fig. 4, but indicating the specific structure of a humidity regulator; Fig. 6 is a schematic perspective view, partly in section, of a combination oven according to a second embodiment of the present invention; Fig. 7 is a view similar to Fig. 5, but according to a third embodiment of the present invention; Fig. 8 is a view similar to Fig. 5, but according to a fourth embodiment of the present invention; Fig. 9 is a view similar to Fig. 5, but according to a fifth embodiment of the present invention; Fig. 10 is a view similar to Fig. 5, but according to an sixth embodiment of the present invention; Fig. 11 is a block diagram of an oven according to a seventh embodiment of the present invention; Fig. 12 is a schematic vertical sectional view of the oven of Fig. 11; Fig. 13A is a horizontal sectional view of a steam generator mounted in the oven of Fig. 12; Fig. 13B is a vertical sectional view of the steam generator of Fig. 13A; Figs. 14A and 14B are views similar to Figs. 13A and 13B, respectively,, but indicating a modification thereof; Figs. 15A and 15B are views similar to Figs. 13A and 13B, respectively,, but indicating another modification thereof; Fig. 16A is a horizontal sectional view of a heater mounted in the oven of Fig. 12; Fig. 16B is a vertical sectional view of the heater of Fig. 16A; Fig. 17 is a circuit diagram of an inverter circuit mounted in the oven of Fig. 12; and Fig. 18 is a sequence diagram in controlling the heating temperature in the oven of Fig. 12. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, several embodiments of the present invention are hereinafter described in detail. The terms "humidified cooking" and "dehumidified cooking" as employed throughout this specification are defined as cooking food while the food is being humidified, and cooking food while the food is being dehumidified, respectively. (Embodiment 1) In Fig. 4, reference numeral 1 denotes food, reference numeral 2 an oven cavity for accommodating the food 1, and reference numeral 3 a heater employed as means for heating the food 1. Also, reference numeral 4 denotes a humidity regulating means for regulating the amount of steam contained in the oven cavity 2, reference numeral 5 a cooking method selecting means for selecting a cooking method, and reference numeral 6 a control unit for controlling the heater 3 and the humidity regulating means 4 on the basis of a signal from the cooking method selecting means 5. In the above-described construction, when the cooking method is selected by the cooking method selecting means 5 after the food 1 has been accommodated in the oven cavity 2, the control unit 6 energizes the heater 3 and controls the humidity regulating means 4 in response to the signal from the cooking method selecting means 5. That is, when the food 1 is heated by radiation or convective heat transfer effected by the heater 3, steam is evaporated from the food 1. In this event, the amount of steam contained in the oven cavity 2 is regulated by the humidity regulating means 4 and, hence, the food surface is neither damp nor dry, so that tasty food in favorable finish can be presented. Fig. 5 depicts an oven accommodating a humidity regulating means 4 in which an adsorbent is employed. In Fig. 5, reference numeral 13 denotes an internal suction port facing the oven cavity 2, reference numeral 14 an external suction port facing the outside of the oven cavity 2, reference numeral 15 a suction duct for communicating between the internal suction port 13 and the external suction port 14, and reference numeral 16 a suction port switching member provided in the suction duct 15. Also, reference numeral 17 denotes an internal discharge port facing the oven cavity 2, reference numeral 18 an external discharge port facing the outside of the oven cavity 2, reference numeral 19 a discharge duct for communicating between the internal discharge port 17 and the external discharge port 18, and reference numeral 20 a discharge port switching member provided in the discharge duct 19. Further, reference numeral 21 denotes a communication duct for communicating between the suction duct 15 and the discharge duct 19, reference numeral 22 an adsorbent such as silica gel, zeolite or the like, reference numeral 23 a blower for sending air to the adsorbent 22, and reference numeral 24 a heat source for supplying thermal energy to the adsorbent 22. In the above-described construction, upon placement of food 1 inside the oven cavity 2, when "dehumidified cooking" or "humidified cooking" is selected by the cooking method selecting means 5, the control unit 6 energizes the heater 3 and controls the humidity regulating means 4 so that the food 1 may be heated while the interior of the oven cavity 2 is being dehumidified or humidified. When dehumidifying and heating are performed, prior to cooking or at the end of cooking, a regeneration process for removing moisture from the adsorbent 22 is followed by a cooking process. That is, in the regeneration process, the control unit 6 operates the suction port switching member 16 and the discharge port switching member 20 to open the external suction port 14 and the external discharge port 18, respectively. The control unit 6 then supplies the heat source 24 with electric power, and operates the blower 23. In this case, air sucked in from the external suction port 14 is heated by the heat source 24 and is sent to the adsorbent 22. When the heated air passes through the adsorbent 22, the moisture contained therein is removed therefrom, and the air is discharged from the external discharge port 18. In the dehumidified cooking process, the control unit 6 operates the suction port switching member 16 and the discharge port switching member 20 to open the internal suction port 13 and the internal discharge port 17, respectively, and also operates the blower 23. Then, air in the oven cavity 2 containing steam generated from the food 1 is sent from the internal suction port 13 to the adsorbent 22, which in turn converts such air to dry air by adsorbing moisture from the former. The dry air is sent to the oven cavity 2 through the internal discharge port 17. Because the adsorbent 22 adsorbs the moisture contained in the food 1, the food 1 can be heated while the oven cavity 2 is being dehumidified. As a result, the surface of food such as tempura and fried food can be dried, thus providing crisp and tasty food. In the case of humidified cooking, prior to cooking or at the end of cooking, a moisture adsorbing process in which moisture contained in air is adsorbed by the adsorbent 22 is followed by a humidified cooking process. That is, in the moisture adsorbing process, the control unit 6 operates the suction port switching member 16 and the discharge port switching member 20 to open the external suction port 14 and the external discharge port 18, respectively, and also operates the blower 23. In this case, the air sucked in from the external suction port 14 is sent to the adsorbent 22 by the blower 23, and moisture contained in the air is adsorbed by the adsorbent 22, and dried air is discharged from the external discharge port 18. In the humidified cooking process, the control unit 6 operates the suction port switching member 16 and the discharge port switching member 20 to open the internal suction port 13 and the internal discharge port 17, respectively. Also, the control unit 6 supplies the heat source 24 with electric power and operates the blower 23. In this case, air sucked in from the internal suction port 13 is heated by the heat source 24, and is sent to the adsorbent 22. When the heated air passes through the adsorbent 22, the moisture adsorbed by the adsorbent 22 is transferred thereto, and hot and damp air is sent into the oven cavity 2 from the internal discharge port 17. In this way, by effectively utilizing the moisture adsorbed by the adsorbent 22, the food 1 can be heated while the interior of the oven cavity 2 is being humidified with a simple construction not requiring supply of water or treatment of drain water. Accordingly, for example, in cooking Chinese cake or dumpling, tasty food can be presented without drying or hardening the food surface. As described above, dehumidified cooking or humidified cooking can be selected depending on the type of food, thus providing tasty food. (Embodiment 2) Fig. 6 depicts a combination oven having a suction port 7, a discharge port 8, and a circulation duct 9 for communicating between the suction port 7 and the discharge port 8. In Fig. 6, reference numeral 30 denotes a door for selectively opening and closing the oven cavity 2 (as a matter of course, the ovens as discussed above also has a door). Inside the circulation duct 9 are provided an adsorbent 22 such as silica gel, zeolite or the like, a blower 23 for sending air to the adsorbent 22, and a heat source 24 such as, for example, an electric heater for feeding thermal energy to the adsorbent 22. Electric power is supplied to the blower 23 and the heat source 24 from a power source 31, and the control unit 6 controls the power source 31 on the basis of a signal from the cooking method selecting means 5 for selecting any one of "humidified cooking" and "dehumidified cooking" depending on information from a sensor. The cooking method can be selected manually. In the above-described construction, when "humidified cooking" is selected by the cooking method selecting means 5, prior to cooking or at the end of cooking, moisture in the air is adsorbed by the adsorbent 22 during the moisture adsorbing process, which is followed by the humidified cooking process. That is, in the moisture adsorbing process, on the basis of the signal indicative of "humidified cooking" selected manually or automatically by the cooking method selecting means 5, the control unit 6 operates the blower 23 without supplying electric power to the heat source 24 so that the moisture may be adsorbed by the adsorbent 22. In the humidified cooking process, the control unit 6 supplies electric power to the heat source 24 and operates the blower 23. In this case, air sucked in through the suction port 7 is heated by the heat source 24 and is turned into hot air. When the hot air passes through the adsorbent 22, it removes the moisture from the adsorbent 22. Because of this, hot and damp air is sent into the oven cavity 2 from the discharge port 8, thereby humidifying and heating the food 1 in the oven cavity 2. On the other hand, when "dehumidified cooking" is selected by the cooking method selecting means 5, the regeneration process for removing the moisture from the adsorbent 22 is first effected prior to cooking, and the dehumidified cooking process is subsequently effected. More specifically, in the regeneration process, the control unit 6 supplies electric power to the heat source 24 and operates the blower 23. In this case, when high-temperature air produced by the heat source 24 passes through the adsorbent 22, it takes the moisture away from the adsorbent 22, and damp air is discharged from the oven cavity 2 when the door 30 is opened. In the dehumidified cooking process, the control unit 6 operates the blower 23 to heat the food 1 while controlling the heat source 24 so that the air passing the heat source 24 may not remove the moisture from the adsorbent 22. At this moment, steam generated from the food 1 during cooking is led to the adsorbent 22 from the suction port 7 and is adsorbed by the adsorbent 22. As a result, the humidity in the oven cavity 2 is maintained low, thus realizing dehumidified cooking. In addition to the above-described construction, one or both of an electric heating means 3 such as, for example, an infrared ray heater, and a high-frequency supply means 32 such as, for example, a magnetron, may be provided near the oven cavity 2. In this case, in the humidified cooking process, the control unit 6 supplies electric power to the heat source 24, operates the blower 23, and also operates the heating means 3 or the high-frequency supply means 32, thereby realizing humidified cooking under the optimum heating condition. On the other hand, in the dehumidified cooking process, the control unit 6 operates the blower 23 and the heating means 3 or the high-frequency supply means 32, thereby realizing dehumidified cooking under the optimum heating condition. (Embodiment 3) Fig. 7 depicts a combination oven having a suction port 7, a discharge port 8, and a waveguide 9a for supplying high frequency. The waveguide 9a corresponds to the circulation duct for communicating between the suction port 7 and discharge port 8. Inside the waveguide 9a are provided an adsorbent 22 such as silica gel, zeolite or the like, a blower 23 for sending air to the adsorbent 22, and a high-frequency supply means 32 such as, for example, a magnetron for supplying high-frequency energy into the oven cavity 2 through the waveguide 9a. Because the other structure is substantially the same as that shown in Fig. 8, description thereof is omitted for brevity's sake. Electric power is supplied to the blower 23 and the high-frequency supply means 32 from the power source 31. The control unit 6 controls the power source 31 on the basis of a signal from the cooking method selecting means 5 for selecting any one of "humidified cooking" and "dehumidified cooking" depending on information from a sensor. The cooking method can be selected manually. In this construction, when "humidified cooking" is selected by the cooking method selecting means 5, prior to cooking or at the end of cooking, moisture in the air is adsorbed by the adsorbent 22in the moisture adsorbing process, which is followed by the humidified cooking process. That is, in the moisture adsorbing process, on the basis of the signal indicative of "humidified cooking" selected manually or automatically by the cooking method selecting means 5, the control unit 6 operates the blower 23 without supplying electric power to the high-frequency supply means 32 so that the moisture may be adsorbed by the adsorbent 22. In the humidified cooking process, the control unit 6 supplies electric power to the high-frequency supply means 32 and operates the blower 23. In this case, the high frequency removes the moisture from the adsorbent 22. The removal of the moisture by the high frequency is effected within a short period of time because water molecules are vibrated directly. For example, when a high-frequency output of 700 W is supplied to a molded material of zeolite processed in corrugated form, about 40 g of moisture can be removed within about 60 seconds. The moisture removed from the adsorbent 22 is sucked in from the suction port 7, and is sent into the oven cavity 2 from the discharge port 8 together with the air led into the waveguide 9a. Moreover, the high frequency supplied into the oven cavity 2 through the suction port 7 or the discharge port 8 as a supply port and through the waveguide 9a heats the food 1, thereby realizing humidified cooking. On the other hand, when "dehumidified cooking" is selected by the cooking method selecting means 5, prior to cooking, the regeneration process is first effected to remove the moisture from the adsorbent 22, and the dehumidified cooking process is subsequently effected. That is, in the regeneration process, the control unit 6 supplies electric power to the high-frequency supply means 32 and operates the blower 23. In this case, the high frequency removes the moisture from the adsorbent 22 within a short period of time, as mentioned above. The moisture removed from the adsorbent 22 is sucked in from the suction port 7, and is sent into the oven cavity 2 through the discharge port 8 together with the air led into the waveguide 9a. The moisture is then discharged outside when the door 30 is opened. In the dehumidified cooking process, while controlling the high-frequency output, the control unit 6 operates the blower 23. By so doing, the high frequency is supplied into the oven cavity 2 through the suction port 7 or the discharge port 8, and steam generated from the food 1 during heating is led to the adsorbent 22 through the suction port 7, and is adsorbed by the adsorbent 22 in order to maintain the humidity inside the oven cavity 2 low, thereby realizing dehumidified cooking. The construction shown in Fig. 7 and having the heating means 3 above the oven cavity 2 enables humidified or dehumidified cooking under the optimum heating condition, as in Embodiment 1. (Embodiment 4) In this embodiment. in addition to the effects mentioned in Embodiment 3 above, the moisture adsorption and regeneration processes are effected arbitrarily. To this end, moisture is entrapped inside the oven cavity 2 directly from air outside the oven cavity 2 in the moisture adsorbing process, and steam is directly discharged outside the oven cavity 2 in the regeneration process. Fig. 8 depicts a microwave oven having an oven cavity 2 defined therein for accommodating food 1 therein and a door 30 for selectively opening and closing the oven cavity 2. This oven also has an internal suction port 13 and an internal discharge port 17 both facing the oven cavity 2, and an external suction port 14 and an external discharge port 18 both facing the outside of the oven cavity 2. The oven further has a suction duct 15 accommodating a suction port switching member 16, and a discharge duct 19 accommodating a discharge port switching member 20. The suction port switching member 16 operates to open either the internal suction port 13 or the external suction port 14, while the discharge port switching member 20 operates to open either the internal discharge port 17 or the external discharge port 18. The suction duct 15 and the discharge duct 19 communicate with each other through a waveguide 9a. The external suction port 14 and the external discharge port 18 are provided with respective microwave cut-off means such as, for example, perforated plates. Inside the waveguide 9a are provided an adsorbent 22 such as, for example, silica gel, zeolite or the like, a blower 23 for sending air to the adsorbent 22, and a high-frequency supply means 32 such as, for example, a magnetron for supplying high-frequency energy into the oven cavity 2 through the waveguide 9a. A power source 31 supplies the blower 23 and the high-frequency supply means 32 with electric power, and a control unit 6 controls the power source 31 on the basis of a signal from the cooking method selecting means 5, which selects any one of "humidified cooking" and "dehumidified cooking" depending on information from a sensor. The cooking method can be selected manually. The control unit 6 also controls the operation of the suction port switching member 16 and that of the discharge port switching member 20. In the above-described construction, when "humidified cooking" is selected by the cooking method selecting means 5, prior to cooking or at the end of cooking, moisture in the air is adsorbed by the adsorbent 22 in the moisture adsorbing process, which is followed by the humidified cooking process. That is, in the moisture adsorbing process, on the basis of the signal indicative of "humidified cooking" selected manually or automatically by the cooking method selecting means 5, the control unit 6 controls the suction port switching member 16 and the discharge port switching member 20 to open the external suction port 14 and the external discharge port 18, respectively, as shown in Fig. 8. Also, as is the case with Embodiment 3, the control unit 6 operates the blower 23 without supplying the high-frequency supply means 32 with electric power so that moisture may be adsorbed by the adsorbent 22. In the humidified cooking process, the control unit 6 controls the suction port switching member 16 and the discharge port switching member 20 to move to respective positions as indicated by dotted lines in Fig. 8, thereby opening the internal suction port 13 and the internal discharge port 17, respectively. Then, humidified cooking is effected, as in Embodiment 3. On the other hand, when "dehumidified cooking" is selected by the cooking method selecting means 5, the moisture contained in the adsorbent 22 is removed therefrom in the regeneration process prior to cooking, and this regeneration process is followed by the dehumidified cooking process. In the regeneration process, the control unit 6 controls the suction port switching member 16 and the discharge port switching member 20 to be positioned as indicated by solid lines in Fig. 10, and the adsorbent 22 is regenerated as in Embodiment 3. In the dehumidified cooking process, the control unit 6 controls the suction port switching member 16 and the discharge port switching member 20 to be positioned as indicated by dotted lines in Fig. 8 so that dehumidified cooking is effected as in Embodiment 3. If the construction shown in Fig. 8 is additionally provided with the heating means 3 above the oven cavity 2, humidified or dehumidified cooking is effected under the optimum heating condition, as in Embodiment 2. A circulation duct separate from the waveguide 9a may be provided additionally. (Embodiment 5) This embodiment aims at humidified or dehumidified cooking, by feeding an optimum amount of moisture into the oven cavity 2 within a short period of time. To this end, the microwave oven is provided, inside the waveguide 9a, with a high-frequency control means 34, which is comprised of, for example, a pair of pivotally arranged perforated plates. The high-frequency control means 34 allows air sent from the blower 23 to the adsorbent 22 to pass therethrough, but prevents high-frequency generated by the high-frequency supply means 32 from reaching the adsorbent 22. Cooking is effected by operating the high-frequency control means 34 on the basis of a signal from the control unit 6. In the case of humidified cooking, on the basis of the signal indicative thereof selected manually or automatically by the cooking method selecting means 5, the control unit 6 performs the moisture adsorbing process, and then the humidified cooking process. In the moisture adsorbing process, the control unit 6 operates the blower 23 without supplying the high-frequency supply means 32 with electric power so that the moisture may be adsorbed by the adsorbent 22. In the humidified cooking process, as shown in Fig. 9, the control unit 6 sets the high-frequency control means 34 at a position where high frequency is supplied to the adsorbent 22, supplies the high-frequency supply means 32 with electric power, and operates the blower 23. Therefore, the moisture adsorbed by the adsorbent 22 can be sent, as steam, into the oven cavity 2 within a short period of time, and the high frequency supplied into the oven cavity 2 through the waveguide 9a and through the suction port 7 or the discharge port 8 heats and cooks the food 1. In the case of dehumidified cooking, on the basis of the signal from the cooking method selecting means 5, the control unit 6 controls, prior to cooking, the high-frequency supply means 32 to remove the moisture from the adsorbent 22 within a short period of time. This regeneration process is followed by the dehumidified cooking process. More specifically, in the regeneration process, as shown in Fig. 9, the control unit 6 sets the high-frequency control means 34 at a position where high frequency is supplied to the adsorbent 22, feeds electric power to the high-frequency supply means 32, and operates the blower 23. In the dehumidified cooking process, the control unit 6 sets the high-frequency control means 34 at a position where no high frequency is supplied to the adsorbent 22, as indicated by dotted lines in Fig. 9. The control unit 6 then operates the blower 23 and feeds electric power to the high-frequency supply means 32. Accordingly, while enabling high-frequency heating, the steam generated from the food 1 during cooking is adsorbed by the adsorbent 22, thus realizing dehumidified cooking. In the case of heating with high frequency alone by stopping supply of steam into the oven cavity 2, the control unit 6 sets the high-frequency control means 34 at the position where no high frequency is supplied to the adsorbent 22, and electric power is supplied to the high-frequency supply means 32. Because only the high frequency is supplied into the oven cavity 2, simple high-frequency heating is effected. (Embodiment 6) Fig. 10 depicts a combination oven having substantially the same construction as the oven shown in Fig. 8, but differs therefrom in that the oven of Fig. 10 is provided, inside the waveguide 9a, with a high-frequency control means 34 such as, for example, a pair of pivotally arranged perforated plates. The high-frequency control means 34 allows air sent from the blower 23 to pass therethrough, but cuts off high-frequency supplied from the high-frequency supply means 32. Cooking is effected by operating the high-frequency control means 34 on the basis of a signal from the control unit 6. When humidified cooking is effected, the operation of each element in the moisture adsorbing process and in the cooking process is the same as that according to Embodiment 4 or 5. Also, when dehumidified cooking is effected, the operation of each element in the regeneration process and in the cooking process is the same as that according to Embodiment 4 or 15. By the construction shown in Fig. 10, moisture is entrapped inside the oven cavity 2 directly from air outside the oven cavity 2 in the moisture adsorbing process, and steam is discharged outside directly from the oven cavity 2 in the regeneration process so that each of the moisture adsorbing process and the regeneration process may be effected arbitrarily, thereby realizing humidified or dehumidified cooking in which the amount of moisture inside the oven cavity 2 is properly regulated. (Embodiment 7) Fig. 11 is a block diagram of a microwave oven. In Fig. 11, steam generated by a steam generator 40 is sent to a heater 42 by a conveying means 41, and is heated to a specified temperature. The heater 42 is controlled by a temperature regulator 44 provided in a control unit 6a, and is designed to heat the steam to the specified temperature. The steam heated to the specified temperature by the heater 42 is supplied into the oven cavity 2 through a valve A 45. The steam exhausted from the oven cavity 2 passes through a valve B 47 and returns to the conveying means 41, thereby forming a circulation path as shown in the diagram. Each of the valve A 45 and the valve B 47 is employed as a path switching means. A temperature sensor 48 detects the temperature of the steam heated by the heater 42, and sends a detection signal to the control unit 6a. On the basis of this signal, the temperature regulator 44 controls the heater 42 with its heating electric energy adjusted properly. A status sensor 49 detects at least one of the temperature, humidity, and pressure of gas generated by food 1 to be heated in the oven cavity 2, or at least one of those of the interior of the oven cavity 2. The status sensor 49 sends a detection signal to the control unit 6a. The control unit 6a controls, on the basis of this detection signal, the steam generator 40, the conveying means 41, the heater 42, the valve A 45 and the valve B 47 so that the food 1 may be properly heated by the steam. The valve A 45 and the valve B 47 employed as the path switching means are intended to form not only a circulation path indicated by solid lines, but also a path indicated by dotted lines to allow air or steam to flow between the interior and the exterior of the oven cavity 2. More specifically, the control unit 6a controls the valve A 45 and the valve B 47 to discharge or introduce the air from or into the circulation path, or to discharge excessive steam therefrom so that the state of the gas inside the oven cavity 2 such as the pressure, gas components or the like may be optimum and safe for heating of the food 1. Fig. 12 depicts a specific structure of the microwave oven of Fig. 11. In Fig. 12, the oven cavity 2 is selectively opened and closed by the door 30 through which the food 1 can be put in and out easily. When the door 30 is closed, the oven cavity 2 is properly sealed by a packing 52 attached along the outer edge of the internal surface of the door 30 in order to prevent the steam from escaping from between the door 30 and the oven cavity 2, thereby avoiding burns by high-temperature steam, or trouble of the appliance due to condensation water of steam. A fan 41 employed as the conveying means sends air to the steam generator 40 and conveys steam generated thereby. The steam generator 40 comprises an adsorption unit 53 including a magnetic material and an adsorbent such as, for example, zeolite, and a heating coil 54 for induction-heating the adsorption unit 53. The detailed structure of the steam generator 40 is described later. The steam generated by the steam generator 40 is sent to and heated by the heater 42. The heater 42 comprises a heat generation unit 55 made of honeycomb-shaped stainless sheets having a large number of passages defined therein, and a heating coil 56 for induction-heating it. The control unit 6a controls the electric power to the heater 42 on the basis of a steam temperature signal detected by the temperature sensor 48. The steam thus heated to a desired temperature is sent into the oven cavity 2 through the valve A 45, as indicated by solid line arrows in the diagram, and diffuses from above to below in the oven cavity 2 to reach the food 1 at a uniform temperature and a uniform flow velocity, thereby heating the food 1 with steam favorably. From a lower portion of the oven cavity 2, a circulation path to return to the fan 41 through the valve B 47 is formed. At the start or end of operation of the appliance, the control unit 6a controls the valve A 45 and the valve B 47 in order to replace steam inside the oven cavity 2 and in the circulation path with air outside the oven cavity 2, or to discharge the steam therefrom so that an appropriate exchange of air and steam may be effected between the outside and the circulation path, as indicated by arrows in the diagram. When it is necessary to take in external air in order for the zeolite of the adsorption unit 53 to adsorb moisture contained therein, the control unit 6a controls the valve A 45 and the valve B 47 to form a path as indicated by the dotted lines in the diagram. Reference numeral 57 denotes a cooling fin, which cools the heating coils 54 and 56 and the control unit 6a to guarantee safety and reliability. Figs. 13A and 13B depict the steam generator 40 having a cylindrical shape, in which the adsorption unit 53 is composed of a molded material containing zeolite particles and iron powder mixed with each other. The zeolite adsorbs water molecules. The iron powder is induction-heated by the heating coil 54, and heats the zeolite to provide the water molecules with thermal energy so that the water molecules adsorbed thereby may be released as steam. An outer tube 58 and a bobbin 59 are interposed between the adsorption unit 53 and the heating coil 54 so as to encircle the adsorption unit 53. The outer tube 58 is made of ceramic or other non-magnetic material, while the bobbin 59 is made of ceramic to insulate and hold the heating coil 54, thus avoiding overheating of the heating coil 54 and enhancing the efficiency to heat the adsorption unit 53. The adsorption unit 53 may be a mixture of adsorptive particles of zeolite and aluminum particles, or may be of a structure containing zeolite particles in honeycomb-shaped or concentrically arranged cylindrical sheets made of stainless steel or aluminum. Figs. 14A and 14B depict a modification of the steam generator 40. The steam generator of Figs. 14A and 14B differs from that of Figs. 13A and 13B in that the former has no heating coil, but has two electrodes 60a and 60b between which the adsorption unit 53 is sandwiched. In this case, upon energization of the two electrodes 60a and 60b, the metallic particles or the metallic structure of the adsorption unit 53 is directly energized and heat the zeolite particles by electric resistance, thus providing substantially the same effects as mentioned above. Figs. 15A and 15B depict another modification of the steam generator 40, which contains zeolite particles 53a encircled by the outer tube 58 and the ceramic bobbin 59. A ring-shaped sheathed heater 61, employed as an exciting means, is disposed below the zeolite particles to release water molecules adsorbed by the zeolite particles 53a. In applications where the exciting means makes use of induction heating or resistance heating, it is sufficient if an adsorbent such as zeolite and a magnetic or metallic material are combined with each other. In contrast, in applications where neither induction heating nor resistance heating is employed, it is sufficient if thermal energy is applied to the adsorbent using a sheathed heater or the like. Figs. 16A and 16B depict the heater 42, which comprises a heat generation unit 55 made of thin stainless steel plates having a honeycomb-shaped lattice structure. In these figures, steam flows in a direction longitudinally of the heater 42. The heat generation unit 55 is held by an insulating outer tube 62 made of, for example, non-magnetic ceramic, while the insulating outer tube 62 is encircled by a ceramic bobbin 63, which holds and insulates the heating coil 56 wound therearound. The configuration of the heating coil 56 and the heat generation unit 55 is designed to guarantee uniform heating by the heat generation unit 55 and insulate it sufficiently. It is, therefore, difficult to provide a high electrical coupling between the heating coil 56 and the heat generation unit 55, and the coupling coefficient is about 0.7 to 0.8. The same is true for the coupling coefficient between the heating coil 54 and the adsorption unit 53 of the steam generator 40 shown in Fig. 13A. Fig. 17 depicts an inverter circuit 70 suited for use in driving the induction coil 54 or 56 at a high efficiency. The inverter circuit of Fig. 17 is supplied with electric power from a commercial power source 72 and comprises a rectifier 73, an inductor 74, a capacitor 75, a resonant capacitor 76, a transistor 77, and a diode 78. The resonant capacitor 76 and the heating coil 54 (56) compose a resonant circuit and, hence, works as a resonant type inverter circuit. An output of the inverter circuit 70 is supplied to the heating coil 54 (56) as high-frequency current of, for example, 20 to 100 kHz, thus induction-heating the adsorption unit 53 and heat generation unit 55. Furthermore, the heating coil 54 (56) has a low coupling coefficient for its structure as mentioned above, causing a considerably large leakage inductance. However, such a resonant type inverter circuit renders the loss of the transistor 77 or the like to be low, realizing a highly efficient electric power conversion. Hence, the steam generator 40 or the heater 42 employing such induction heating can be raised in efficiency. In Fig. 17, reference numerals 79 and 80 compose a detection circuit required for a drive circuit 81 to drive the transistor 77 in synchronism with the resonant circuit mentioned above. Reference numerals 82 and 83 denote an amplifier and a current detector, respectively, which are intended to stabilize the electric power supplied from the inverter circuit 70 to the adsorption unit 53 or the heat generation unit 55. Reference numeral 84 denotes control terminals, which receives control signals from the control unit 6a. The oven of the above-described construction effects cooking as shown in, for example, Fig. 18 under the control of the control unit 6a. In the case of food A, it is heated and dried by dry steam at 200°C simultaneously with start of cooking. After specified drying, finish heating is done for a short period of time with low-temperature steam at 80°C, thus terminating cooking. In the case of food B, it is overheated with a slightly overheated steam at 120°C and is dried at 170°C, until the cooking process is terminated. In the case of food C, it is heated with low-temperature steam at 60°C and is further heated with overheated steam at 170°C immediately before the cooking process is terminated. Thus, the oven according to the present invention can heat and cook food by appropriately adjusting the steam temperature depending on the kind and quantity of food, thus optimizing cooking according to the material to be cooked. In the foregoing embodiments, although zeolite is used as the adsorbent, the adsorbent is not limited thereby, and any material can be used if it has superior water absorption properties and is safe in sanitation. A porous body having continuous foams and made of ceramics or plastics may be used as the adsorbent. Alternatively, a fibrous body made of paper, ceramic fiber, plastic fiber, natural fiber of paper or cotton, or their laminate may be used. Also, ceramics, plastics or the like which has undergone water absorption treatment can be used. However, if the adsorbent is brought into contact with overheated steam, the material thereof must be selected in consideration of heat resistance. The adsorption unit 53 may be encircled by any one of the outer tube 58 and the ceramic bobbin 59 (heat resistant bobbin) depending on the construction. Furthermore, although the heater has been discussed as having honeycomb-shaped stainless steel sheets containing a large number of passages defined therein, it is not limited thereby. It is sufficient if the heater is made of a conductor having a large number of through-holes defined therein. If a heating method other than induction heating is employed, the heater may be made of a material having a high thermal conductivity and also having a large number of through-holes defined therein. Moreover, the heater is not limited to the honeycomb-shaped structure, and a lattice or any other structure may be employed as far as through-holes are formed therein.

Claims: An oven having an oven cavity (2) defined therein in which food (1) to be cooked is to be accommodated, said oven comprising: a food heating means (3) for heating the food (1) accommodated in the oven cavity (2); a humidity regulating means (4; 40, 42) for regulating a humidity inside the oven cavity (2); a cooking method selecting means (5) for selecting a cooking method; and a control means (6) for controlling said humidity regulating means (4) in response to a signal from said cooking method selecting means (5) to selectively humidify and dehumidify an interior of the oven cavity (2); characterized in that said humidity regulating means (4; 40, 42) comprises adsorption means (22; 42) for absorbing or emitting steam contained in the air. The oven according to claim 1, wherein said adsorption means (22; 40) comprises an adsorbent (22; 53) having water absorption properties. The oven according to claim 1 or 2, further comprising a heater (24; 42) interposed between the oven cavity (2) and said adsorption means (22; 40). The oven according to anyone of claims 1 to 3, wherein said humidity regulating means comprises an internal suction port (13) facing the oven cavity (2), an internal discharge port (17) facing the oven cavity (2), a circulation duct (21) for communicating said internal suction port (13) and said internal discharge port (17) with each other, a blower (23) for sending air to said adsorption means (22), and a heat supply means (24) for supplying said adsorption means (22) with thermal energy, and wherein said adsorption means (22) is accommodated in said circulation duct (21). The oven according to anyone of claims 1 to 3, wherein said humidity regulating means (4) comprises an internal suction port (13) facing the oven cavity (2), an external suction port (14) facing an outside of the oven cavity (2), a suction duct (15) for communicating said internal suction port (13) and said external suction port (14) with each other, a suction port switching member (16) accommodated in said suction duct (15), an internal discharge port (17) facing the oven cavity (2), an external discharge port (18) facing the outside of the oven cavity (2), a discharge duct (19) for communicating said internal discharge port (17) and said external discharge port (18) with each other, a discharge port switching member (20) accommodated in said discharge duct (19), a communication duct (21) for communicating said suction duct (15) and said discharge duct (19) with each other, a blower (23) for sending air to said adsorption means (22), and a heat supply means (24) for supplying said adsorption means (22) with thermal energy, and wherein said adsorption means (22) is accommodated in said communication duct (21). The oven according to anyone of claims 1 to 3, wherein said humidity regulating means (4) comprises an internal suction port (13) facing the oven cavity (2), an internal discharge port (17) facing the oven cavity (2), a circulation duct (21) for communicating said internal suction port (13) and said internal discharge port (17) with each other, a blower (23) for sending air to said adsorption means (22), and a high-frequency supply means (32) for supplying said adsorption means (22) with high frequency, and wherein said adsorption means (22) is accommodated in said circulation duct (21). The oven according to anyone of claims 1 to 3, wherein said adsorption means (40) contains one of a magnetic material and a metallic material, wherein said humidity regulating means (4) comprises an exciting means (61) for applying thermal energy to said one of the magnetic material and the metallic material, and wherein energization of said exciting means (61) renders said adsorption means to emit moisture adsorbed thereby to generate steam. The oven according to claim 7, wherein said exciting means (61) comprises an induction-heating means.

Inventors: FUJITANI YOSHITOMO, MAEHARA NAOYOSHI, MORIGUCHI MIKI, MORIYA YOSHIFUMI, YANAGIDA NAOKO, YONENO NORIYUKI, FUJITANI, YOSHITOMO, MAEHARA, NAOYOSHI, MORIGUCHI, MIKI, MORIYA, YOSHIFUMI, YANAGIDA, NAOKO, YONENO, NORIYUKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: H05B6
IPC codes: A21B3, H05B6